Supercritical fluid cleaning of semiconductor substrates

ABSTRACT

Chemical formulations and methods for removing unwanted material, such as unexposed photoresist, metal oxides, CMP residue, and the like, from semiconductor wafers or other substrates. The formulations utilize a supercritical fluid-based cleaning composition, which may further include (I) co-solvent(s), (II) surfactant(s), (III) chelating agent(s), and/or (IV) chemical reactant(s).

FIELD OF THE INVENTION

[0001] The present invention relates generally to chemical techniquesused in semiconductor wafer fabrication, and particularly, to chemicalformulations and methods using supercritical fluids to remove unwantedmaterial such as photoresists, metal oxides and residues fromsemiconductor substrates during semiconductor wafer processing.

DESCRIPTION OF THE RELATED ART

[0002] Photolithography is used to structurally define the patterns ofthe layers and doping regions on semiconductor wafers. Photolithographytechniques comprise the steps of coating, exposure, and development.Initially, a wafer is coated with a negative or positive photoresistsubstance and subsequently covered with a mask that defines specificareas to be either retained or removed in subsequent processes.Following the proper positioning of the mask, the photoresist layer(negative) is irradiated to harden the exposed photoresist materialthereby making it resistant to removal and/or etching. The non-exposedphotoresist material is then removed, or “developed,” thereby leavingbehind a pattern identical to the mask. Effective removal of theunwanted negative or positive photoresist is crucial because incompleteremoval of the non-exposed photoresist residue affects subsequentprocesses and compromises the quality of the finished semiconductordevice.

[0003] At present, the favored technique to remove the developedphotoresist is plasma ashing. Plasma ashing involves exposing thephotoresist-covered wafer to oxygen plasma in order to oxidativelydecompose the unexposed photoresist film from the substrate surface.However, plasma etching usually results in the formation ofplasma-etching residue, and this residue must subsequently be removed bywet chemical treatment. During wet chemical treatment, the wafertypically is exposed to solutions containing cleaning solvents andcorrosion-inhibiting amines. Notably, it is difficult to balanceeffective plasma-etching residue removal and corrosion inhibitionbecause the residue and the wafer layers tend to be similar materials.As such, unwanted removal of desired layers or corrosion of metal layersoften occurs. Additionally, the use of copious amounts of cleaningagents and solvents presents environmental and safety issues andinvolves substantial costs for proper handling and disposal of thesechemical reagents. On the other hand, when the device criticaldimensions become very small, it is difficult for wet chemical topenetrate into deep trenches and vias because of the high surfacetension. As a result, incomplete cleaning will occur. SCF has near zerosurface tension and thus enables the complete cleaning for smalldimension vias and trenches.

[0004] It therefore would be advantageous to provide a developmentprocess that effectively removes unwanted photoresist material andresidue, without the disadvantages associated with conventionalphotoresist removal techniques.

[0005] More generally, it would be highly advantageous to provide ameans and method for removal of unwanted material from a semiconductorwafer, e.g., photoresist, metal oxide, chemical mechanical planarization(CMP) residues, etc. during wafer processing.

SUMMARY OF THE INVENTION

[0006] The present invention relates to chemical formulations andmethods for removing unwanted material, e.g., unexposed photoresist,metal oxides, CMP residues, etc., from semiconductor wafers. Theformulations of the invention utilize a supercritical fluid (SCF), ashereinafter more fully described.

[0007] In one aspect, the invention relates to a cleaning formulationuseful for removing unwanted material from a surface having suchunwanted material thereon, said cleaning formulation comprising asupercritical fluid, at least one co-solvent, and at least oneadditional active agent.

[0008] Another aspect of the invention relates to a semiconductor wafercleaning formulation useful to remove non-exposed photoresist from asemiconductor wafer surface having irradiated and non-irradiatedphotoresist regions thereon, such formulation comprising an additive orco-solvent in supercritical media.

[0009] A further aspect of the invention relates to a cleaningformulation for removing unwanted solid deposited material from asurface of a substrate having the unwanted solid deposited materialthereon, such cleaning formulation comprising:

[0010] (I) a supercritical fluid comprising a fluid species selectedfrom the group consisting of carbon dioxide, oxygen, argon, water,ammonia, and mixtures thereof; and

[0011] (II) a co-solvent species selected from the group consisting ofmethanol, ethanol, and higher alcohols, N-alkylpyrrolidones, e.g.,N-methyl-, N-octyl-, or N-phenylpyrrolidones, dimethylsulfoxide,sulfolane, catechol, ethyl lactate, acetone, butyl carbitol,monoethanolamine, butyrol lactone, diglycol amine, alkyl ammoniumfluoride, γ-butyrolactone, butylene carbonate, ethylene carbonate, andpropylene carbonate.

[0012] In yet another aspect, the invention relates to a method forfabricating a semiconductor wafer. The method comprises the removal ofunwanted material from the surface of the wafer with a cleaningformulation comprising a supercritical fluid, at least one co-solvent,and at least one additional active agent.

[0013] A still further aspect of the invention relates to a method ofremoving non-exposed photoresist from a semiconductor wafer surfacehaving irradiated and non-irradiated photoresist regions thereon,comprising contacting the semiconductor wafer surface with an additiveor co-solvent in supercritical media.

[0014] The invention in another aspect relates to drying of exposed andaqueous developed photoresist patterns without image collapse ordegradation.

[0015] In another aspect, the invention relates to a method for removingunwanted solid deposited material from a surface of a substrate havingthe unwanted solid deposited material thereon, comprising contacting thesubstrate surface with a cleaning formulation comprising

[0016] (I) a supercritical fluid comprising a fluid species selectedfrom the group consisting of carbon dioxide, oxygen, argon, krypton,xenon, ammonia, and mixtures thereof, and

[0017] (II) a co-solvent species selected from the group consisting ofmethanol, ethanol, and higher alcohols, N-alkylpyrrolidones, such asN-methyl-, N-octyl-, or N-phenylpyrrolidones, dimethylsulfoxide,sulfolane, catechol, ethyl lactate, acetone, butyl carbitol,monoethanolamine, butyrol lactone, diglycol amine, alkyl ammoniumfluoride, γ-butyrolactone, butylene carbonate, ethylene carbonate, andpropylene carbonate.

[0018] Another aspect of the invention relates to a method of integratedcircuit (IC) manufacture on a semiconductor substrate, comprisingcleaning the semiconductor substrate to remove organic and/or inorganicmaterial present thereon, wherein such cleaning comprises contacting thesemiconductor substrate with a supercritical fluid-based cleaningcomposition including at least one of (I) co-solvent(s), (II)surfactant(s), (III) chelating agent(s), and (IV) chemical reactant(s).

[0019] A further method aspect of the invention relates to a method ofintegrated circuit (IC) manufacture on a semiconductor substrate,comprising cleaning the semiconductor substrate to remove organic and/orinorganic material present thereon, wherein such cleaning comprisescontacting the semiconductor substrate with a supercritical fluid-basedcleaning composition to permeate same into the material, and heating thesemiconductor substrate to induce removal of the material therefrom bythe action of the supercritical fluid-based cleaning composition.

[0020] Another aspect of the invention relates to a method of integratedcircuit (IC) manufacture on a semiconductor substrate, comprisingcleaning the semiconductor substrate to remove organic and/or inorganicmaterial present thereon, wherein such cleaning comprises contacting thesemiconductor substrate with a supercritical fluid-based cleaningcomposition in a pulsed mode of operation involving intermittentadministration of energy to the cleaning composition on thesemiconductor substrate.

[0021] A further aspect of the invention relates to a method of removingnon-irradiated photoresist from a semiconductor wafer surface havingirradiated and non-irradiated photoresist regions thereon, comprisingcontacting the semiconductor wafer surface with an etching agent in thepresence of a supercritical fluid.

[0022] The invention further relates to a method of removing water ordrying a lithographic pattern, after exposure and aqueous development,without image collapse or degradation.

[0023] In another method aspect, the invention relates to a method ofcleaning a printed circuit board of unwanted metal oxides thereon,comprising contacting the printed circuit board surface and/or contactvias with a cleaning formulation comprising an acid dissolved in asupercritical fluid.

[0024] The invention relates in a further aspect to a method of cleaninga surface of unwanted material deposited thereon, comprising contactingthe surface with a cleaning formulation comprising a reducing agent in asupercritical fluid.

[0025] A further aspect of the invention relates to a method of surfacetreatment of a substrate to produce a modified surface amenable tofurther processing, such method comprising contacting the substratesurface with a modifying composition comprising a supercritical fluidand at least one surface-modifying component effective to change thechemical properties of the substrate surface, or to protect underlyingmaterial or structure associated with such substrate surface.

[0026] A still further aspect of the invention relates to a surfacemodification composition for modifying the chemical properties of asubstrate surface or to protect underlying material or structureassociated with the substrate surface, said composition comprising anSCF and a long-chain organic material.

[0027] A further aspect of the invention relates to a method of removingwater from a substrate after development of aqueous developedphotoresist thereon, without image collapse or degradation, comprisingcontacting the substrate with a cleaning composition containing asupercritical fluid and at least one additional component selected fromthe group consisting of co-solvent(s), active agent(s), surfactant(s)and chelating agent(s).

[0028] In another aspect, the invention relates to a compositioncomprising CO₂ and at one semiconductor processing etchant, wherein saidCO₂ and said at least one semiconductor processing etchant are presentin said composition as supercritical fluids.

[0029] Yet another aspect of the invention relates to a cleaningcomposition, comprising supercritical CO₂, isopropanol, and ammoniumfluoride.

[0030] A still further aspect of the invention relates to a method ofcleaning a semiconductor substrate to remove unwanted materialtherefrom, said method comprising contacting the semiconductor substratewith a cleaning composition comprising supercritical CO₂, isopropanol,and ammonium fluoride.

[0031] Other aspects, features and embodiments of the invention will bemore fully apparent from the ensuing disclosure and appended claims.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF

[0032] Supercritical fluids are formed under conditions at which thedensity of the liquid phase equals the density of the gaseous phase ofthe substance. For example, carbon dioxide (CO₂), which is a gas atstandard temperature and pressure, undergoes a transition from liquid toSCF above a critical point, corresponding to Tc≧31.1° C. and p_(c)≧72.8atm. Once formed, the density of the SCF can be varied from liquid-liketo gaseous-like, yielding different solvation abilities, by varying thepressure and temperature. Supercritical fluids have a density/solubilityand diffusibility approaching that of the liquid and gaseous phase,respectively. Additionally, the surface tension of SCFs is negligible.

[0033] Because of its readily manufactured character, ability to berecycled, lack of toxicity and negligible environmental effects,supercritical CO₂ is a preferred SCF in the broad practice of thepresent invention, although the invention may be practiced with anysuitable SCF species, with the choice of a particular SCF depending onthe specific application involved.

[0034] The present invention relates to supercritical fluid-basedcleaning compositions for removal of unwanted material fromsemiconductor wafers. In specific embodiments, the cleaning compositionsinclude at least one of (I) co-solvent(s), (II) surfactant(s), (III)chelating agent(s), and (IV) chemical reactant(s).

[0035] For example, pure SCF, such as supercritical CO₂ may be effectivein some applications without any additional components, e.g., where theunwanted material on the semiconductor substrate is soluble in orotherwise completely removed by the supercritical CO₂. In otherapplications, the SCF may not be an effective solvent for the removal ofthe unwanted material from the semiconductor substrate. In such case,the addition of appropriate co-solvent(s) may be employed to increasethe solubility and removability of the photoresist material and residuein the SCF.

[0036] Alternatively, SCFs in combination with other components, such assurfactants, chelating agents and/or chemical reactants such asacids/bases or oxidants/reductants are contemplated in the practice ofthe invention to effect material removal. The use of additionalcomponents in the SCF-based formulation can be exploited to enhance thecleaning action of the composition, e.g., by manipulating the criticaltemperature of the mixture, or by introducing polar or nonpolarconstituents to the formulation in order to enhance the interactions ofthe cleaning formulation with a specific compound or material sought tobe removed from the semiconductor substrate.

[0037] Due to the progressively smaller dimensions of semiconductorpatterns, the SCF-based cleaning formulations of the invention provide adistinct advantage in penetrating small geometry structures such as viasand trenches on the semiconductor wafer, particularly in instances inwhich the wettability of the semiconductor substrate is low. This samefeature allows the removal of H₂O from aqueous developed photoresists of<0.09 μm characteristic dimension, without image collapse ordegradation.

[0038] The cleaning formulations of the invention thus may be variouslyformulated with SCF(s), co-solvent(s), active agent(s), surfactant(s)and chelating agent(s).

[0039] In one aspect, the cleaning composition comprises an SCF, aco-solvent, and an active agent, for removal of unexposed photoresist,metal oxides, CMP residues, etc. Surface metal oxides pose a particularproblem in semiconductor manufacturing electrodeposition operations, inthat they can prevent proper nucleation of electroplated deposits andinterfere with electrical conductivity.

[0040] In another aspect, the cleaning composition comprises an SCF, aco-solvent, an active agent, surfactant(s) and/or chelating agent(s), asnecessary or desirable for removal of specific unwanted material on thesemiconductor substrate.

[0041] Examples of SCF species useful in the broad practice of theinvention include, but are not limited to, carbon dioxide, oxygen,argon, krypton, xenon, or ammonia.

[0042] An “active agent” as used herein is a material that induceschemical reaction, either in the cleaning composition as a reactionmixture, or at the surface of the semiconductor wafer, to enhance thecleaning and/or removal action of the formulation, relative to acorresponding formulation lacking such material.

[0043] Examples of active agents include, without limitation, acids,bases, reducing agents and oxidizing agents. Illustrative active agentsinclude HF sources (e.g., HF, triethylamine trihydrogen fluoride,hydrogen fluoride-pyridine, etc.), fluoride sources (e.g., of theformula R₄NF, wherein each R is independently selected from H, alkyl,aryl, etc., wherein alkyl is preferably C₁-C₈ alkyl and aryl ispreferably C₆-C₁₂ aryl) perfluorocarboxylic acids, alkyl sulfonic acids,aryl sulfonic acids, alkyl amines, ozone, dinitrogen oxide, potassiumpermanganate, and hydrogen.

[0044] Preferably, the active agent is an acid or a reducing agent. Whena reducing agent is solubilized in the SCF, the reducing agent mayrequire activation, e.g., by an activation process involving thermal,optical, and/or sonic activation.

[0045] Co-solvent species useful in the cleaning formulations of theinvention may be of any suitable type. Illustrative species, include,but are not limited to, methanol, ethanol, and higher alcohols,N-alkylpyrrolidones, such as N-methyl-, N-octyl-, orN-phenylpyrrolidones, dimethylsulfoxide, sulfolane, catechol, ethyllactate, acetone, butyl carbitol, monoethanolamine, butyrol lactone,diglycol amine, alkyl ammonium fluoride, ybutyrolactone, butylenecarbonate, ethylene carbonate, and propylene carbonate.

[0046] Surfactants useful in the cleaning formulations of the presentinvention may likewise be of any suitable type, including anionic,neutral, cationic, and zwitterionic types. Illustrative surfactantspecies include, without limitation, acetylenic alcohols and diols, andlong alkyl chain secondary and tertiary amines.

[0047] Chelating agents useful in the cleaning formulations of theinvention may be of any suitable type, including, for example,polycarboxylic acids such as iminodiacetic acid and laurylethylenediamine triacetic acid, β-diketones such as: 2,4-pentanedione;1,1,1trifluoro-2,4-pentanedione; and1,1,5,5,5-hexafluoro-2,4-pentanedione, substituted dithiocarbamates,malonic acid esters, and polyethylene glycols.

[0048] Illustrative species of acids useful in the cleaning formulationsof the invention include, without limitation, perfluorocarboxylic acids,and alkyl or aryl sulfonic acids. Illustrative species of bases usefulin the cleaning formulations of the invention include, but are notlimited to, amines, such as alkyl amines. Oxidizing agents useful in thebroad practice of the invention include, without limitation, oxygen,ozone and nitrous oxide.

[0049] Reducing agents usefully employed in the cleaning formulations ofthe invention include, without limitation, hydrogen, ammonia, silanes,hydrides and metal hydrides.

[0050] The components of (I) co-solvent(s), (II) surfactant(s), (III)chelating agent(s), and (IV) chemical reactant(s), when present in theSCF-based cleaning formulations of the present invention, may be presentat any suitable concentrations and relative proportions, as appropriateto the use of the formulation in removing unwanted material from asubstrate surface having such unwanted material deposited thereon.

[0051] For example, the components (I)-(IV) may be present atconcentrations of from about 0.1% by weight to about 50% by weight, whenpresent in the formulation, or alternatively in concentration rangeshaving minima such as 0.2%, 0.5%, 1% and 5%, and maxima such as 25%,20%, 18%, 15%, 12% and 10%, in any permutative combinations thereof.

[0052] Further, the cleaning formulations of the invention mayselectively comprise, consist of, or consist essentially of, any of theSCF and optionally additional components of the formulation disclosedherein. The weight percentage concentrations of components of thecleaning formulation as referred to herein, are based on the totalweight of the formulation, including the SCF(s) and all othercomponents.

[0053] Another aspect of the invention relates to using traditionaletching gases, such as, for example, sulfur hexafluoride (SF₆), carbontetrafluoride (CF₄) and xenon difluoride (XeF₂), in a supercritical formto achieve higher etch rates than are achievable by conventional etchprocesses, and also to avoid the need for plasmas to activate theetching species. To stimulate the etch reaction using such supercriticaletching gases, thermal activation or radiation can be used. The SCF,e.g., SF₆ or CF₄, can be used neat or in combination with other SCFs.Additionally, co-solvent(s), surfactant(s), chelating agent(s), and/oractive agent(s) can be added to the supercritical etchant cleaningformulation.

[0054] Another aspect of the present invention relates to a method forfabricating a semiconductor wafer, in which photoresist, CMP residuesand/or metal oxide substances are removed from the semiconductor waferusing an SCF-containing cleaning formulation, e.g., a cleaningformulation comprising a mixture of at least one supercritical fluid, atleast one co-solvent, and at least one additional active agent.

[0055] The methods and cleaning formulations of this invention areadvantageous for removing unwanted substrate materials, such asphotoresists, metal oxides and CMP residues. Due to the high wettingcharacter of the SCF, which allows it to penetrate small and complexgeometries on the semiconductor wafer, the SCF is able to effect a highrate and extent of cleaning of the semiconductor substrate.Additionally, smaller quantities of toxic reagents are needed and moresubstantial cleaning of the substrate surface is achieved by theSCF-based cleaning formulations of the invention, relative to theprocedures and compositions heretofore conventionally used in the art.

[0056] As a specific example, a semiconductor wafer in a semiconductordevice manufacturing facility may be subjected to initial masking andphotoresist radiation exposure, following which the semiconductor waferis loaded and sealed in a process vessel. The process vessel is purgedwith a process gas that corresponds to the SCF gas but is at anon-supercritical condition, to displace all other gases in the vessel.In a specific embodiment, the process gas is CO₂, and the correspondingSCF used in the process is supercritical CO₂. Typically, when CO₂ isused, the gaseous pressure of the CO₂ purge gas does not exceed about 2atm. After purging, the vessel is heated to a temperature T_(o)>T_(c)and is pressurized to a pressure p_(o)>p_(c) with preheated CO₂. Thedesired pressure, p_(o), and temperature, T_(o), are dependent on thewafers to be cleaned, the chemical formulation and process parameters,the material to be removed from the wafer, and the process equipmentthat is employed. Once p_(o) and T_(o) are attained, the process vesselis charged with supercritical CO₂.

[0057] The semiconductor wafer cleaning formulation may comprise suchCO₂ alone, or more preferably a mixture of supercritical fluid CO₂, aco-solvent, and at least one additional active agent. The semiconductorwafer cleaning formulation is introduced to the vessel to removeunwanted material, e.g., photoresist, from the wafer. The cleaningoperation is continued for sufficient time to effect substantiallycomplete removal of the unwanted material from the wafer surfaces.

[0058] The contacting of the semiconductor wafer with the SCF-basedsemiconductor wafer cleaning formulation, or “soaking” of the wafer inthe cleaning formulation, is carried out for a suitable period of time,which in a specific embodiment can for example be on the order of fromabout 20 to about 60 seconds, although other (longer or shorter) periodsof contacting may be usefully employed depending on the nature andamount of the material to be removed from the semiconductor wafer, andthe process conditions employed for wafer cleaning.

[0059] During the contacting with the wafer, the semiconductor wafercleaning formulation at high pressure infuses into the unwanted surfacematerial, e.g., photoresist, to cause swelling of the surface andweakening of the interface bonds. The semiconductor wafer cleaningformulation thus may be formulated to dissolve specific fluorinatedcompounds, metal oxides, or other coatings, layers or residues, toeffect their removal from the substrate. Thus, for example, a reducingagent may be incorporated in the semiconductor wafer cleaningformulation, and activated during the wafer contacting step by suitable(e.g., thermal, optical, and/or sonic) activation techniques.

[0060] Following soaking of the wafer in the semiconductor wafercleaning formulation, the vessel containing the wafer is rapidlydecompressed while maintaining the process fluid in the vessel in asupercritical state. During decompression, the unwanted material on thesubstrate, which was weakened in the soaking step, is subjected to asudden pressure differential to cause such unwanted material to breakaway from the substrate. The unwanted material components that aresolubilized in the semiconductor wafer cleaning formulation in thehigher pressure soaking step may drop out of solution in the lowerpressure decompressed state and be readily collected for disposal, orsuch components may remain in solution and be readily removed from thepressure vessel by exhausting the unwanted material-containingsemiconductor wafer cleaning formulation from the pressure vessel.

[0061] The above-mentioned decompression step may be conducted for anysuitable period of time, e.g., on the order of 20 seconds, althoughlonger or shorter times may be desirable depending on the character ofthe material to be removed from the semiconductor wafer surfaces and thespecifics of the process. If necessary, repeated cycles of soaking anddecompression may be utilized to achieve substantially complete removalof the unwanted material from the semiconductor wafer.

[0062] Following removal of the unwanted material, the wafer is rinsedwith pure supercritical CO₂ for a suitable period of time, e.g., for 30seconds. Thereafter, the vessel is dried so that the wafer can beremoved. This is effected by maintaining the vessel temperature atT_(o)>T_(c) and decreasing the pressure as T_(o) remains constant. Thesupercritical CO₂ under such conditions will transform directly into thegaseous phase without entering the liquid phase, thereby eliminating therisk of residual liquid droplet stains on the wafer.

[0063] The cleaning process of the invention can be practiced withvariable pressure processing, or alternatively it can be carried out atconstant or substantially constant pressure, with the residue on thesubstrate reacting and dissolving in the SCF solution, and not justphysically peeling from the surface of the substrate.

[0064] In another aspect of the invention, etching gases such as sulfurhexafluoride, carbon tetrafluoride or xenon difluoride are utilized in asupercritical state for enhancement of etching to effect materialremoval, e.g., of photoresist, metal oxides, CMP residue, etc., from thesemiconductor substrate.

[0065] In yet another variant aspect of the invention, supercritical SF₆and/or supercritical CF₄ can be mixed with supercritical CO₂, optionallywith co-solvent(s) and the aforementioned active agents, analogous tothe previously described semiconductor wafer cleaning formulations ofthe invention.

[0066] The etching gases utilized in such SCF-based cleaningformulations may be activated during the substrate contacting step byconventional activation techniques, such as thermal, optical and/orsonic activation techniques.

[0067] According to yet another embodiment of the invention, asupercritical fluid can be driven into the unwanted material film on thesemiconductor substrate during an initial contacting step, followed byapplication of heat to the SCF-penetrated substrate film to effectexpansion of the SCF, e.g., CO₂, and resultant lift-off of the unwantedmaterial film from the substrate. The contacting conditions areappropriately selected to uniformly distribute the SCF over thesubstrate surface, so that the SCF is substantially homogeneouslydissolved in the film.

[0068] Upon application of heat, rapid expansion of the SCF, e.g., CO₂,occurs, causing disruption, degradation and decomposition of theunwanted material, e.g., photoresist, film. The SCF contacting andheating steps may be repetitively carried out as necessary to effectremoval of any residual unwanted material on the semiconductorsubstrate. Alternatively, wet cleaning agents may be applied to theSCF-treated surface to complete the removal of residual material, orsuch wet cleaning treatment may be followed by renewed SCF treatment. Itwill be appreciated that such use of SCF may be combined with otherunwanted material removal agents and approaches, as necessary ordesirable in a given application to yield substantially complete removalof the unwanted material from the semiconductor substrate.

[0069] The present invention broadly contemplates the enhancement ofcurrently employed semiconductor wafer etchant materials by use of SCFat the etching locus, to facilitate transport of the etchant into finefeature areas of the semiconductor substrate. Such augmentation of theetching technique enables effective pattern definition, e.g., of highaspect ratio vias and trenches, to be achieved. Such use of SCF agentsin combination with established etching agents also overcomes issuesassociated with low etch rates, and thereby enables etchants to be used,which would otherwise be of low or marginal utility due to theirinadequate permeation or penetration into the material layer or residueon the substrate surface.

[0070] Further, the invention contemplates the use of traditionaletching agents such as SF₆, CF₄, etc. in supercritical form themselves,e.g., in a neat SCF form, or in combination with other SCF agents, suchas CO₂, etc., to achieve etching rates and extent of removal of unwantedsubstrate material, which are substantially in excess of thoseachievable by conventional processes, and without the need for plasmaactivation of the etchant.

[0071] Etchant compositions in accordance with the invention encompassformulations including the use of chelating agents dissolved in thesupercritical fluid. Thermal activation and other activation modalitiescan be employed to stimulate the etching reaction, e.g., UV lightexposure and/or laser energy impingement on the etch site. These opticalactivation methods may be employed in any suitable manner, such as byflood exposure through a mask, or by projection onto a surface to effectnon-contact selective etching.

[0072] The invention also contemplates pulsed operation in such etchapplications, where the activating radiation is pulsed forhigh-efficiency etching action with a high degree of control, inrelation to conventional dip/spray wet etching techniques.

[0073] The invention also contemplates use of SCF-based compositions tomodify surface charge of a substrate to assist removal of unwantedmaterial thereon, or to effect a protective action on the substrate.Thus, SCF-based compositions containing materials capable of binding tothe substrate surface, or to selected surface regions thereof, can beemployed to change the chemical properties of the surface, or to protectthe underlying material or structure. The modifying components of thecomposition may be any suitable type, as for example high molecularweight materials having relatively low volatility (which low volatilitycharacteristic renders such high molecular weight materials difficult oreven impossible to transport by conventional deposition methods such aschemical vapor deposition).

[0074] By use of supercritical fluids, such modifying materials can bereadily solubilized, transported efficiently to the substrate to bemodified, and contacted with the substrate. Thereafter, the substratecan be rapidly dried and subsequently processed in the same processchamber, e.g., by cleaning processes, deposition processes, etc.

[0075] When the surface modification is employed to effect protectiveaction on the substrate surface or a selected region thereof, theprotected surface (as modified by the modifying agent) can subsequentlybe returned to its original state, such as by contacting of thesubstrate with another SCF-based composition containing a cleaningcomponent, and/or by ordinary liquid phase cleaning chemistry afterremoval of the substrate element from the process chamber.

[0076] Such methodology permits the delivery of different materials,e.g., modifying/protective materials, other deposited materials,cleaning agents, etc., to the substrate using the same processequipment, thereby facilitating high through-put processing in thesemiconductor manufacturing facility.

[0077] In a specific embodiment, long-chain materials constitute themodifying component. Such long-chain modifying components include,without limitation, long-chain organothiols, long-chain acetates andlong-chain amines. Such long-chain organic materials can be bound toselected surface regions on the substrate to vary surface chemicalproperties, and/or to protect the contacted region of the substrate forsubsequent processing. Long-chain materials can be applied to thesubstrate surface in specific embodiments for reversible sorption on thesurface, such sorbed material being stable in subsequent processingsteps, or alternatively, conferring on the coated substrate an enhancedcleanability, as appropriate to the specific application. Thus, asubstrate surface may be modified to render it more highly susceptibleto cleaning, in subsequent interaction with cleaning compositions, e.g.,SCF-based compositions, conventional wet cleaning agents, and the like.

[0078] As used herein, the term “long-chain” in reference to organicmaterials used for surface modification or surface protection, means achain having at least eight atoms therein, e.g., from eight to fortyatoms. In specific embodiments, the long-chain molecules may compriseC₈-C₄₀ chains, C₈-C₃₀, or other carbon number ranges appropriate to thespecific substrate and surface modification/surface protection functionto be effected by the long-chain agent.

[0079] Substrates in the practice of the invention may be formed of anysuitable material of construction. Illustrative substrate materialsinclude, without limitation, silicon, sapphire, gallium arsenide,gallium nitride, silicon on insulator (SOI), and silicon carbide.

[0080] More generally, the present invention is susceptible of use in awide variety of applications. By way of further specific example,SCF-assisted etching in accordance with the present invention may beutilized for cleaning of recording head sides of printed circuit boards(PCBs). Thus, SCF-based etching compositions and techniques of theinvention may be employed for removal of surface oxides from coppersurfaces prior to the plating of the recording head. The removal ofsurface oxides is necessary in such applications, since unremovedsurface oxide deposits prevent good nucleation of electroplated depositsand interfere with electrical conductivity of the recording head.

[0081] A cleaning formulation can be made up by dissolving anappropriate acid medium in a supercritical fluid, and then dispensingsame onto the contact surface of the PCB substrate. The wetting abilityimparted by the supercritical fluid to the cleaning formulation obviatesor at least minimizes the need for surfactant(s) in the cleaningformulation.

[0082] In another embodiment, hydrogen or other reductive species aredissolved in a supercritical fluid and activated at the surface to becleaned. The activation may be effected in any suitable manner, e.g.,thermally, optically or by means of sound waves (e.g., ultrasonically ormegasonically), to reduce surface copper oxides and facilitate theirremoval from the PCB surface.

[0083] The invention may be carried out in a pulsed process wherein thecleaning medium includes the supercritical solvent, optionally with anetchant component or reductive agent. In such pulsed process, thecleaning medium is alternatingly and repetitively energized by thermal,optical and/or sonic means to effect the cleaning of the substrate.

[0084] The present invention is broadly applicable to integrated circuit(IC) manufacture, for cleaning operations between successive processsteps to remove organic and/or inorganic residues that are present, suchas photoresist or post-etch photoresist products.

[0085] By the provision of a supercritical fluid-based cleaningcomposition including at least one of (I) co-solvent(s), (II)surfactant(s), (III) chelating agent(s), and (IV) chemical reactant(s),the cleaning compositions and corresponding cleaning methods of thepresent invention facilitate removal of unwanted material inapplications where low solubility and low wettability of the material tobe removed would otherwise not be satisfactorily addressed by the SCFalone or by various combinations of (I)-(IV) without such SCF component.

[0086] Thus, the SCF-based cleaning compositions of the presentinvention permit effective cleaning of small size structures ofsemiconductor substrates, and have the further advantage that theyeliminate the need for large quantities of liquid aqueous and organicreagents such as are used in conventional cleaning operations. As aresult, the large volume waste streams from the semiconductormanufacturing facility that are generated by prior art cleaningtechniques are avoided.

[0087] In the practice of the present invention, after the cleaningoperation has been concluded, the (I) co-solvent(s), (II) surfactant(s),(III) chelating agent(s), and (IV) chemical reactant(s) are readilyseparated from the cleaning formulation due to the large difference invapor pressure between the SCF and the other component(s) (I)-(IV).

[0088] The features and advantages of the invention are more fullyapparent from the following example.

EXAMPLE

[0089] Post ash photoresist residue was removed from the surface ofpatterned structures by the following process. A cleaning composition,including alcohol (e.g., methanol, ethanol, isopropanol) co-solvent insupercritical CO₂ and a fluorinated agent, was added to a cleaningvessel and allowed to equilibrate at 4000 psi at 90° C. (1% w/vfluoride, 15% w/v alcohol). The cleaning fluid composition wascirculated through the cleaning vessel at a constant pressure andtemperature for a predetermined period of time (30-900 seconds). Uponcompletion, the cleaning composition was displaced with puresupercritical CO₂ and the cleaning vessel was rinsed with three volumesamount of supercritical CO₂ in order to completely remove the cleaningcomposition from the wafer surface.

[0090] In general, cleaning formulations of such type were found to behighly effective in compositions including (i) the supercritical fluidCO₂, (ii) isopropanol in an amount of from about 0.005 wt. % to about 20wt. %, based on the weight of the composition, and (iii) ammoniumfluoride in an amount of from about 0.005 wt. % to about 5.0 wt. %,based on the weight of the composition, when such formulations wereutilized for cleaning contact with the substrate for a time period offrom about 30 to about 900 seconds, at suitable temperature, e.g., onthe order of about 90° C.

[0091] It will be appreciated that the compositions and cleaning andetch removal methods of the invention may be practiced in a widelyvariant manner, consistent with the broad disclosure herein.Accordingly, while the invention has been described herein withreference to specific features, aspects, and embodiments, it will berecognized that the invention is not thus limited, but is susceptible ofimplementation in other variations, modifications and embodiments.

[0092] Accordingly, the invention is intended to be broadly construed toencompass all such other variations, modifications and embodiments, asbeing within the scope of the invention hereinafter claimed.

What is claimed is:
 1. A cleaning formulation useful for removingunwanted material from a surface having such unwanted material thereon,said cleaning formulation comprising a supercritical fluid, at least oneco-solvent, and at least one additional active agent.
 2. The cleaningformulation according to claim 1, wherein the supercritical fluidcomprises a fluid selected from the group consisting of: carbon dioxide,oxygen, argon, ammonia, and mixtures thereof.
 3. The cleaningformulation according to claim 1, wherein the supercritical fluidcomprises carbon dioxide.
 4. The cleaning formulation according to claim1, wherein said at least one co-solvent comprises a co-solvent selectedfrom the group consisting of: methanol, ethanol, isopropyl alcohol,N-methylpyrrolidone, N-octylpyrrolidone, N-phenylpyrrolidone,dimethylsulfoxide, sulfolane, catechol, ethyl lactate, acetone, butylcarbitol, monoethanolamine, butyrol lactone, diglycol amine, alkylammonium fluoride, ybutyrolactone, butylene carbonate, ethylenecarbonate, and propylene carbonate.
 5. The cleaning formulationaccording to claim 1, further comprising at least one surfactant.
 6. Thecleaning formulation according to claim 5, wherein the at least onesurfactant comprises a surfactant selected from the group consisting of:3,4-dimethyl-1-hexyn-3-ol and 2,4,7,9-tetramethyl-5-decyn-4,7-diol. 7.The cleaning formulation according to claim 1, further comprising atleast one chelating agent.
 8. The cleaning formulation according toclaim 7, wherein the at least one chelating agent comprises a chelatingagent selected from the group consisting of: iminodiacetic acid, laurylethylenediamine triacetic acid, 2,4-pentanedione,1,1,1-trifluoro-2,4-pentanedione,1,1,1,5,5,5-hexafluoro-2,4-pentanedione, substituted dithiocarbamates,malonic acid esters, and polyethylene glycols.
 9. The cleaningformulation according to claim 1, wherein said at least one additionalactive agent comprises an acid that is effective to remove metal oxidematerial when same is present as the unwanted material on said surface.10. The cleaning formulation according to claim 9, wherein said acid isselected from the group consisting of: perfluorocarboxylic acids, alkylsulfonic acids, and aryl sulfonic acids.
 11. The cleaning formulationaccording to claim 1, wherein the active agent comprises a reducingagent that is effective to remove metal oxide material when same ispresent as the unwanted material on said surface.
 12. The cleaningformulation according to claim 11, wherein the reducing agent comprisesan agent selected from the group consisting of hydrogen, ammonia,silanes, hydrides and metal hydrides.
 13. The cleaning formulationaccording to claim 11, wherein the reducing agent is activated by amodality selected from the group consisting of thermal activation,optical activation, and sonic activation.
 14. The cleaning formulationaccording to claim 11, wherein said metal oxide material comprisescopper oxide.
 15. A semiconductor wafer cleaning formulation useful toremove non-irradiated photoresist from a semiconductor wafer surfacehaving irradiated and non-irradiated photoresist regions thereon, saidformulation comprising an etching gas in supercritical form.
 16. Thecleaning formulation according to claim 15, wherein the etching gascomprises an etching agent selected from the group consisting of sulfurhexafluoride, carbon tetrafluoride and xenon difluoride.
 17. Thecleaning formulation according to claim 15, further comprising anothercomponent in supercritical fluid form.
 18. The cleaning formulationaccording to claim 17, wherein the additional supercritical fluidcomponent comprises a fluid species selected from the group consistingof carbon dioxide, oxygen, argon, and ammonia.
 19. The cleaningformulation according to claim 17, wherein the additional supercriticalfluid component comprises carbon dioxide.
 20. The cleaning formulationaccording to claim 17, wherein the formulation is activated by thermaland/or optical activation.
 21. The cleaning formulation according toclaim 15, further comprising a co-solvent.
 22. The cleaning formulationaccording to claim 15, further comprising a surfactant.
 23. The cleaningformulation according to claim 15, further comprising an active agent.24. The cleaning formulation according to claim 15, further comprising achelating agent.
 25. A cleaning formulation for removing unwanted soliddeposited material from a surface of a substrate having the unwantedsolid deposited material thereon, said cleaning formulation comprising(I) a supercritical fluid comprising a fluid species selected from thegroup consisting of carbon dioxide, oxygen, argon, ammonia, and mixturesthereof, and (II) a co-solvent comprising a co-solvent species selectedfrom the group consisting of methanol, ethanol, and higher alcohols,N-alkylpyrrolidones, such as N-methyl-, N-octyl-, orN-phenyl-pyrrolidones, dimethylsulfoxide, sulfolane, catechol, ethyllactate, acetone, butyl carbitol, monoethanolamine, butyrol lactone,diglycol amine, alkyl ammonium fluoride, γ-butyrolactone, butylenecarbonate, ethylene carbonate, and propylene carbonate.
 26. The cleaningformulation of claim 25, further comprising at least one surfactant. 27.The cleaning formulation of claim 25, further comprising at least onesurfactant selected from the group consisting of acetylenic alcohols anddiols, and long alkyl chain secondary and tertiary amines
 28. Thecleaning formulation of claim 25, further comprising at least onechelating agent.
 29. The cleaning formulation of claim 25, furthercomprising at least one chelating agent selected from the groupconsisting of polycarboxylic acids, P-diketones, substituteddithiocarbamates, malonic acid esters, and polyethylene glycols.
 30. Thecleaning formulation of claim 25, further comprising at least onechelating agent selected from the group consisting of iminodiaceticacid, lauryl ethylenediamine triacetic acid, 2,4-pentanedione,1,1,1-trifluoro-2,4-pentanedione,1,1,1,5,5,5-hexafluoro-2,4pentanedione, substituted dithiocarbamates,malonic acid esters, and polyethylene glycols.
 31. The cleaningformulation of claim 25, further comprising at least one active agent.32. The cleaning formulation of claim 25, further comprising at leastone active agent selected from the group consisting of (a) acids, (b)bases, (c) oxidants, and (d) reductants.
 33. The cleaning formulation ofclaim 25, further comprising at least one active agent selected from thegroup consisting of HF sources, fluoride sources, perfluorocarboxylicacids, alkyl sulfonic acids, aryl sulfonic acids, alkyl amines, ozone,dinitrogen oxide, potassium permanganate, and hydrogen.
 34. A method forfabricating a semiconductor wafer, said method comprising removingunwanted material from the surface of the wafer with a cleaningformulation comprising a supercritical fluid, at least one co-solvent,and at least one additional active agent.
 35. The method according toclaim 34, wherein the supercritical fluid comprises a fluid selectedfrom the group consisting of: carbon dioxide, oxygen, argon, ammonia,and mixtures thereof.
 36. The method according to claim 34, wherein thesupercritical fluid comprises carbon dioxide.
 37. The method accordingto claim 34, wherein said at least one co-solvent comprises a cosolventselected from the group consisting of: methanol, ethanol, isopropylalcohol, N-methylpyrrolidone, N-octylpyrrolidone, N-phenylpyrrolidone,dimethylsulfoxide, sulfolane, catechol, ethyl lactate, acetone, butylcarbitol, monoethanolamine, butyrol lactone, diglycol amine, alkylammonium fluoride, γ-butyrolactone, butylene carbonate, ethylenecarbonate, and propylene carbonate.
 38. The method according to claim34, wherein the cleaning formulation includes at least one surfactant.39. The method according to claim 38, wherein the at least onesurfactant comprises a surfactant selected from the group consisting of:3,4-dimethyl-1-hexyn-3-ol and 2,4,7,9tetramethyl-5-decyn-4,7-diol. 40.The method according to claim 34, wherein the cleaning formulationfurther comprises at least one chelating agent.
 41. The method accordingto claim 40, wherein the at least one chelating agent comprises achelating agent selected from the group consisting of: iminodiaceticacid, lauryl ethylenediamine triacetic acid, 2,4-pentanedione,1,1,1-trifluoro-2,4-pentanedione,1,1,1,5,5,5-hexafluoro-2,4-pentanedione, substituted dithiocarbamates,malonic acid esters, and polyethylene glycols.
 42. The method accordingto claim 34, wherein said at least one additional active agent comprisesan acid that is effective to remove metal oxide material when same ispresent as the unwanted material on said surface.
 43. The methodaccording to claim 42, wherein said acid is selected from the groupconsisting of: perfluorocarboxylic acids, alkyl sulfonic acids, and arylsulfonic acids.
 44. The method according to claim 34, wherein the activeagent comprises a reducing agent that is effective to remove metal oxidematerial when same is present as the unwanted material on said surface.45. The method according to claim 44, wherein the reducing agentcomprises an agent selected from the group consisting of hydrogen,ammonia, silanes, hydrides and metal hydrides.
 46. The method accordingto claim 44, wherein the reducing agent is activatable by an activationmodality selected from the group consisting of thermal activation,optical activation, and sonic activation.
 47. The method according toclaim 44, wherein said metal oxide material comprises copper oxide. 48.A method of removing non-irradiated photoresist from a semiconductorwafer surface having irradiated and non-irradiated photoresist regionsthereon, comprising contacting the semiconductor wafer surface with anetching gas in supercritical form.
 49. The method according to claim 48,wherein the etching gas comprises an etching agent selected from thegroup consisting of sulfur hexafluoride, carbon tetrafluoride and xenondifluoride.
 50. The method according to claim 48, wherein the cleaningformulation further comprises another component in supercritical fluidform.
 51. The method according to claim 50, wherein the additionalsupercritical fluid component comprises a fluid species selected fromthe group consisting of carbon dioxide, oxygen, argon, and ammonia. 52.The method according to claim 50, wherein the additional supercriticalfluid component comprises carbon dioxide.
 53. The method according toclaim 48, wherein the cleaning formulation is activatable by thermaland/or optical activation.
 54. The method according to claim 48, whereinthe cleaning formulation further comprises a co-solvent.
 55. The methodaccording to claim 48, wherein the cleaning formulation furthercomprises a surfactant.
 56. The method according to claim 48, whereinthe cleaning formulation further comprises an active agent.
 57. Themethod according to claim 48, wherein the cleaning formulation furthercomprises a chelating agent.
 58. A method for removing unwanted soliddeposited material from a surface of a substrate having the unwantedsolid deposited material thereon, comprising contacting the substratesurface with a cleaning formulation comprising (I) a supercritical fluidcomprising a fluid species selected from the group consisting of carbondioxide, oxygen, argon, ammonia, and mixtures thereof; and (II) aco-solvent comprising a co-solvent species selected from the groupconsisting of methanol, ethanol, and higher alcohols,N-alkylpyrrolidones, such as N-methyl-, N-octyl-, orN-phenyl-pyrrolidones, dimethylsulfoxide, sulfolane, catechol, ethyllactate, acetone, butyl carbitol, monoethanolamine, butyrol lactone,diglycol amine, alkyl ammonium fluoride, γ-butyrolactone, butylenecarbonate, ethylene carbonate, and propylene carbonate.
 59. The methodof claim 58, wherein the cleaning formulation further includes at leastone surfactant.
 60. The method of claim 58, wherein the cleaningformulation further includes at least one surfactant selected from thegroup consisting of acetylenic alcohols and diols, and long alkyl chainsecondary and tertiary amines
 61. The method of claim 58, wherein thecleaning formulation further includes at least one chelating agent. 62.The method of claim 58, wherein the cleaning formulation furtherincludes at least one chelating agent selected from the group consistingof polycarboxylic acids, β-diketones, substituted dithiocarbamates,malonic acid esters, and polyethylene glycols.
 63. The method of claim58, wherein the cleaning formulation further includes at least onechelating agent selected from the group consisting of iminodiaceticacid, lauryl ethylenediamine triacetic acid, 2,4-pentanedione,1,1,1-trifluoro-2,4-pentanedione,1,1,1,5,5,5-hexafluoro-2,4-pentanedione, substituted dithiocarbamates,malonic acid esters, and polyethylene glycols.
 64. The method of claim58, wherein the cleaning formulation further includes at least oneactive agent.
 65. The method of claim 58, wherein the cleaningformulation further includes at least one active agent selected from thegroup consisting of (a) acids, (b) bases, (c) oxidants, and (d)reductants.
 66. The method of claim 58, wherein the cleaning formulationfurther includes at least one active agent selected from the groupconsisting of HR sources, fluoride sources, perfluorocarboxylic acids,alkyl sulfonic acids, aryl sulfonic acids, alkyl amines, ozone,dinitrogen oxide, potassium permanganate, and hydrogen.
 67. A method ofintegrated circuit (IC) manufacture on a semiconductor substrate,comprising cleaning the semiconductor substrate to remove organic and/orinorganic material present thereon, wherein said cleaning comprisescontacting the semiconductor substrate with a supercritical fluid-basedcleaning composition including at least one of (I) co-solvent(s), (II)surfactant(s), (III) chelating agent(s), and (IV) chemical reactant(s).68. A method of integrated circuit (IC) manufacture on a semiconductorsubstrate, comprising cleaning the semiconductor substrate to removeorganic and/or inorganic material present thereon, wherein said cleaningcomprises contacting the semiconductor substrate with a supercriticalfluid-based cleaning composition to permeate same into the material, andheating the semiconductor substrate to induce removal of the materialtherefrom by the action of the supercritical fluid-based cleaningcomposition.
 69. A method of integrated circuit (IC) manufacture on asemiconductor substrate, comprising cleaning the semiconductor substrateto remove organic and/or inorganic material present thereon, whereinsaid cleaning comprises contacting the semiconductor substrate with asupercritical fluid-based cleaning composition in a pulsed mode ofoperation involving intermittent administration of energy to thecleaning composition on the semiconductor substrate.
 70. A method ofremoving non-irradiated photoresist from a semiconductor wafer surfacehaving irradiated and non-irradiated photoresist regions thereon,comprising contacting the semiconductor wafer surface with an etchingagent in the presence of a supercritical fluid.
 71. A method of cleaninga printed circuit board surface of unwanted metal oxides thereon,comprising contacting the printed circuit board surface with a cleaningformulation comprising an acid dissolved in a supercritical fluid.
 72. Amethod of cleaning a surface of unwanted material deposited thereon,comprising contacting the surface with a cleaning formulation comprisinga reducing agent in a supercritical fluid.
 73. The method of claim 72,wherein the cleaning formulation is activated by an activation modalityselected from the group consisting of thermal activation, opticalactivation and sonic activation, to effect cleaning action on thesurface.
 74. The method of claim 72, wherein the unwanted materialcomprises copper oxide.
 75. The method of claim 72, wherein the unwantedmaterial comprises unexposed photoresist.
 76. A method of surfacetreatment of a substrate to produce a modified surface amenable tofurther processing, said method comprising contacting the substratesurface with a modifying composition comprising a supercritical fluidand at least one surface-modifying component effective to change thechemical properties of the substrate surface, or to protect underlyingmaterial or structure associated with such substrate surface.
 77. Themethod of claim 76, wherein the at least one surface-modifying componentcomprises a long-chain organic material.
 78. The method of claim 76,wherein the at least one surface-modifying component comprises at leastone long-chain compound selected from the group consisting of long-chainorganothiols, long-chain acetates and long-chain amines.
 79. The methodof claim 76, wherein the SCF component comprises supercritical CO₂. 80.A surface modification composition for modifying the chemical propertiesof a substrate surface or to protect underlying material or structureassociated with the substrate surface, said composition comprising anSCF and a long-chain organic material.
 81. The composition of claim 80,wherein said long-chain organic material comprises an organic componentselected from the group consisting of long-chain organothiols,long-chain acetates and long-chain amines.
 82. A method of removingwater from a substrate after development of aqueous developedphotoresist thereon, without image collapse or degradation, comprisingcontacting the substrate with a cleaning composition containing asupercritical fluid and at least one additional component selected fromthe group consisting of co-solvent(s), active agent(s), surfactant(s)and chelating agent(s).
 83. The method of claim 82, wherein the aqueousdeveloped photoresist has a dimensional characteristic of <0.09 μm. 84.A composition comprising CO₂ and at one semiconductor processingetchant, wherein said CO₂ and said at least one semiconductor processingetchant are present in said composition as supercritical fluids.
 85. Thecomposition of claim 84, wherein said at least one semiconductorprocessing etchant comprises at least one perfluorocarbon species. 86.The composition of claim 85, wherein said at least one perfluorocarbonspecies comprises at least one of SF₆ and CF₄.
 87. A cleaningcomposition, comprising supercritical CO₂, isopropanol, and ammoniumfluoride.
 88. The cleaning composition of claim 87, wherein isopropanolis present at a concentration of from about 0.005 to about 20 wt. %,based on total weight of the composition.
 89. The cleaning compositionof claim 88, wherein ammonium fluoride is present at a concentration offrom about 0.005 to about 5.0 wt. %, based on total weight of thecomposition.
 90. A method of cleaning a semiconductor substrate toremove unwanted material therefrom, said method comprising contactingthe semiconductor substrate with a cleaning composition comprisingsupercritical CO₂, isopropanol, and ammonium fluoride.
 91. The method ofclaim 90, wherein said contacting is carried out for a duration of up toabout 900 seconds.
 92. The method of claim 90, wherein said contactingis carried out for a duration of from about 30 to about 900 seconds.